Abstract: An elapsed time indicator comprises a reservoir of a fluid, a porous sheet element and a fluid port located between the reservoir and the porous sheet element. The porous sheet element defines a predetermined area which is separated from the fluid port by a predetermined lateral distance. The fluid is selectively provided from the reservoir to the porous sheet element through the fluid port whereupon the porous sheet element transmits the fluid laterally through the porous sheet element at a predetermined rate away from the fluid port until the fluid impregnates the predetermined area of the porous sheet element so as to cause the predetermined area of the porous sheet element to become transparent or more transparent after expiry of a predetermined time period.